In recent years, the need to “know examination results while examining a patient” has increased in clinics and small-scale hospitals, and thus switching from conventional outsourced examination done outside hospitals to Point of Care Testing (POCT) occurs. With the spread of POCT, a device installing an immunochromatographic lateral flow test strip is being used as an in vitro diagnostic product. An immunochromatographic test strip enables detection of an object in a sample, without the need of reagent preparation at the time of testing, through only a simple manipulation such as direct dropping of a test sample (hereinafter, referred to as “sample”) such as blood, urine, etc. onto the test strip, and is very useful for simple and rapid analysis of an analyte.
The immunochromatographic test strip (hereinafter, referred to as “test strip”) is generally a porous membrane including a sample supply portion, a spreading portion, and a detecting portion, and has a structure in which a detection reagent (hereinafter, referred to as “conjugate”) such as a labeled antibody against an analyte, etc. is retained at a spreading start part of the spreading portion in a dissoluble and spreadable manner such that the labeled antibody can pass through the spreading portion and reach the detecting portion after contact with a sample while an immobilized antibody is immobilized at a part of the spreading portion to constitute the detecting portion. When the sample is dropped onto the sample supply portion, the analyte in the sample specifically binds to the labeled antibody to form a complex, and the complex spreads through the spreading portion in the downstream direction and further binds to the immobilized antibody. Thus, by detecting a sandwich-type complex of the labeled antibody, the analyte, and the immobilized antibody in an antibody-immobilization part, the analyte may be qualitatively or quantitatively analyzed. An example of a label constituting a conjugate is colloidal gold particles and a color reaction of the colloidal gold particles enables qualitative detection. The analyte in the sample may also quantitatively be detected, based on a degree of coloring.
However, if the sample is whole blood, red blood cells in the whole blood cannot move in a porous membrane, and will problematically clog pores of the membrane and obstruct spreading of the sample. Therefore, if whole blood is used as a sample, red blood cells must preliminarily be separated and removed from the whole blood, and known methods include a method of removing red blood cells after precipitation through centrifugation before measurement, and a method of filtrating and removing red blood cells agglutinated by a red blood cell-separating agent before measurement or at the start of measurement.
As the red blood cell-separating agent, for example, hexadimethrine bromide (distributed under the trade name of polybrene, hereinafter, simply referred to as polybrene) is known (Patent Documents 1, 2, and 3).
In Patent Document 1, polybrene is described as an example of a hemagglutinating agent made of a synthetic water-soluble polymer.
In Patent Document 2, a glass-fiber blood cell-separating membrane for chromatography containing polybrene as a hemagglutinating substance is described. Since passage of blood through the blood cell-separating membrane is associated with hemolysis when polybrene is solely used, a technique is disclosed for coating the blood cell-separating membrane with PVA for avoiding the hemolysis.
Although polybrene is generally known as a hemagglutinating agent, if polybrene is used for immunochromatography employing a metal conjugate as a detection reagent, polybrene problematically causes not only agglutination of red blood cells in whole blood but also agglutination of the metal conjugate (Patent Document 3).
Patent Document 3 discloses a technique for preventing such agglutination of metal conjugates. That is, disclosed in Patent Document 3 is an immunochromatographic assay device that has a polycation, such as polybrene, etc., as a red blood cell-separating agent bound in the upstream of chromatography supports (carriers) and a polyanion for neutralizing the polycation bound in the downstream thereof. According to this technique, agglutination of metal conjugates made of selenium may be prevented, because the positive charge of the polycation is neutralized by the negative charge of the polyanion.